1. Technical Field
It relates to a metal ink composition for ink-jet and more particularly, a metal ink composition which causes no formation of cracks on a PCB substrate, allows a low temperature curing, and provides improved adhesive strength after coating.
2. Description of the Related Art
Noncontact direct writing technology through inkjet offers advantages in reduction of manufacturing costs and time since it allows ejecting an exact amount of ink to only a desired portion. For applying the inkjet method to form metal wires on a PCB substrate, a metal ink has been greatly developed with growth of interests in the metal ink.
Metal inks in market are a water-based metal ink, a non-water-based metal ink and a solvent-based ink which are divided according to types of solvent. A solvent of metal ink is selected according to a coating material to be used in manufacturing metal nanoparticles. Each ink has advantages and disadvantages. The non-water-based metal ink has a less particle size than the water-based metal ink and allows mass production in high concentration and continuous ejection through a head. However, it causes significant cracks of wires in a printed image and requires a surface treatment due to ununiform CD (critical dimesion) and curing at a high temperature of 250° C. or higher.
Metal nano ink, which is printed on a polyimide, is needed to maintain its adhesive strength and be thus used for printed wires after a coating process in order to be applied for PCB substrates. However, the non-water-based nano ink does not maintain the adhesive strength since a coating solution percolates after printing wires so that it causes delamination of wires and deteriorates mechanical property of wires. Providing appropriate properties as wires is the most important factor in the nano metal ink. Such properties are adhesive strength to a substrate, a low curing temperature and prevention of forming cracks for a metal ink composition. It is the most difficult problem to satisfy such requirements in the development of metal ink composition.